Device for  switching eleotsic



Oct. 3, 1933 t .E. F. NORTHRUP 1,928,629

DEVICE FOR SWITCHING ELECTRIC CURRENTS Filed June 13 1951 FIQ.2

[/7 1/81? for Patented Oct. 3, 1933 UNITED STATES PATEN OFFiCE I messes nsvrca iron swircinnc stcc'rmc @URRE Application June 13, 1931. Serial No. 544,217

3 Claims.

My invention relates to methods and apparatus for switching electric currents and is especial ly useful when used on circuits where the frequency is higher than normal.

A purpose of my invention is to supply a current switching device or connector of hollow section designed to take advantage of the so-called skin eilect of alternating current and to dispense with the section of copper on the inside of the'piece which does not carry a proportionate share of the current.

A further purpose is to increase the current carrying capacity of the switch by passing a cooling medium through its interior to carry away the resistance losses and to prevent overheating of the contact surfaces.

A further purpose is to provide a clamped connection where the switch or connecting piece is connected to the main line, thereby insuring a better contact than could beobtained by a sliding contact depending upon the inherent spring of the switch jaws for pressure.

A further purpose is to use smaller contact lugs and parts, thereby allowing the connectors to be mounted closer together and diminishing their self inductance as a consequence.

A further purpose is to provide a simple, rugged and inexpensive transfer switching device for al= ternating currents.

Further purposes will appear in the specifica= tion and claims.

I have preferred to illustrate my invention by five figures.

Figs. 1 and 2 show the top and front views of a switch embodying my invention.

Fig. 3a is a sectional view of Figs. 1 and 2 taken through the plane A-A.

Fig. 3b is a fragmentary portion of Fig. to showing how the contact part might be adapted for a line rather than a surface contact.

Fig. 4 is a line diagram of an induction furnace circuit showing one application of my invention.

In the drawing similar numerals indicate like parts.

It is well known that alternating currents tend to crowd to the surface. of conductors, and that there is a definite depth of penetration beyond which the addition of copper or conducting material is of little or no value. Even on frequencies as low as those normally supplied to the industry, it has sometimes been advisable to split up the current carrying buses for the better utilization of the carrying capacity, and radiation of heat from the conductor.

As the frequency of the current source is increased, the surface effect becomes more and more pronounced until at frequencies of several hundred thousand cycles there is practically no current flow in the inside layers.

In my work with coreless induction furnaces, this characteristic of the current crowding to the surface has been most troublesome and switches and parts designed by the usual methods have not been adequate for the service required. In order to obtain the necessary sur face area forcarrying the heavy currents it has been necessary to greatly enlarge the bus and switch parts. This has made it necessary to use more copper; to allow more space between bus or switching units; and has increased the eddy current losses which are set up in the larger pieces by the alternating current field.

To offset these disadvantages, I have invented the switch which, referring to the drawing, I shall now describe.

In the figures, l, 2 and 3 are connecting lugs, preferably of copper. They are suitably mounted on an insulating panel board 4, and held in po-- sition by the nuts 5, '5. and 7. Contacts 8, 9 and it, which may he watercooled or not, as desired, are attached to the back of the lugs as shown in Fig. 3a.

The transfer contact or front portion of the lugs are cut out to form a receiver for the con- 83 tact piece 11 which may be clamped in position to make contact between the center bus and either end by means of the clamping screws 12, i2 and 12''.

As shown in the figures, the contact piece 11 is round, but in practice it may be of any irregular section desired. It is shown to be hollow, with hose connections 13 and 13 so that a cool ing fluid or gas may be forced through, during operation, to keep the parts cold. The wall thickness of the part ii, is of such a dimension that when cold, and carrying full current, the PR loss is not greater than would be encountered in a circuit carrying the same amperes at normal frequency. i

Figs. 3c and 3?: show how the lugs may be adapted to give a surface or line contact respectively.

Fig. i I have shown one application of i invention. The generator 14 is arranged to feed alternating current through the switches 15 and 16, the lines 17 and 18, connections 19 and 20 to the inductor or furnace coil 21 or through switches 15 and 16 lines 1'7 and 18 connec tions 19 and 20 to inductor coil 21 1P A single condenser bank 22 is supplied to resonate either furnace coil, and is adapted for connection to the respective coils by means of the water-cooled switch previously described. That is, when the generator is feeding the furnace coil 21, as shown, the resonating condensers are connected to that coil by means of water-cooled connectors 11 and 11 clamped between lugs 2 and 3 and 2 and 3 respectively.

In view of my invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain part or all of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:--

1. A connecting switch for high frequency alternating current circuits comprising connecting lugs on the circuits to be connected, a hollow .tubular artificially cooled connecting piece, and

clamping devices to hold said connecting piece in operative contact with preferred lugs on the circuits to be connected.

2. A connecting switch for alternating current comprising clamping. lugs, a hollow tubular artificially cooled connecting piece, clamped in contact with the center lug and either end lug and means for releasing the clamps to allow the connector to be moved through and out of engagement with one end lug and into engagement with the center and other end lug.

5. A connecting switch for alternating current circuits comprising three clamping lugs, a hollow tubular artificially cooled connecting piece removably clamped in position between a common lug and either of the other lugs and means for releasing said clamps to allow the transfer of said connecting piece and its subsequent connecting between the common lug and the other lug.

6. In a switching device for alternating currents, a plurality of clamping lugs connected to different parts of an electrical system, a hollow tubular artificially cooled connecting piece mak-- ing contact with and clamped to any two of said lugs to complete an electric circuit through the lugs so connected and means for releasing the clamps on said lugs to allow easy transfer of the connecting piece for use with any other selected pair of lugs in the device.

7. In a connecting device for alternating current three clamping lugs placed in a .line, a hollow tubular artificially cooled connecting piece, optionally and removably clamped between the center lug and either end lug but free to slide through all lugs when the latter are unclamped and of length sufficient for making contact with any two lugs.

8. In a connecting device for alternating current two or more clamping lugs placed in a line,

a hollow tubular artificially cooled connecting piece, free to slide through all lugs when the latter are unclamped and means for rigidly hold ing the connector in the lugs when current is passing through it.

EDWIN F. NORTHRUP. 

